Hi Alan,
There's an easy answer, and a harder answer, but lt's start with the easy one. This isn't exactly what you want, but it's close.
1. On the form options - go to the Validation Tab and turn on the option
Wizard : Validate Tab on Next
2. Add some custom embed code to "require" the checkbox to be set. ie, assuming the field is called say Inv:Paid
in the
ValidateValue::Inv:Paid Routine
If Inv:Paid <> 1
loc:invalid = 'Inv:Paid'
loc:alert = 'Please click on the Paid checkbox before continuing'
End
In some ways this is a better solution than just disabling the Next button because it explicitly informs the user what they have to do in order to proceed. Just disabling the Next button prevents them from continuing, but they don't necessarily know why.
If this approach is ok for you, let me know.
cheers
Bruce